I thought this glyph would be a no-brainer for most people.
You get to regen Mana within the time span of one GCD. How could anyone not like that? It doesn't take math or a genius to figure out that 1 GCD (ie, 1.5 seconds) >> 2 seconds of cast time, in which you can't move or anything without breaking the channel.
Glyphed it as soon as I started healing, and I love it, wont change it. I think right now, its cooldown is pretty much stuck in my head, I just mechanically hit it anways, whenever no immediate heal is required.